The present invention relates to a method of producing a porous ceramic panel, and more particularly to a method of producing a porous ceramic panel capable of preventing the generation of open void cells in the panel by pressing and integrating it, and capable of giving a superior surface smoothness to the panel.
Though porous ceramic panels have not yet been used widely, the application thereof for prefabricated houses and the like has been examined because of their lightness, easiness to be handled, and superiority in thermal-insulation, fire-resistance, durability and the like.
Main raw materials for producing the above porous ceramic panels are, in general, natural glass, artificial glass, porous volcanic rock, igneous rock, sedimentary rock, tuff, and the like. The porous ceramic panels are produced by foaming the above raw materials and simultaneously pressing on an upper surface of the foaming body by a belt, or by pressing panels after the foaming step, so as to fuse cells together and shape the foaming or foamed body.
In the case of using a belt, a foaming body in a heating and foaming step (or burning step) is generally pressed by a belt 26 continuously and flatly from an above direction.
In the case of using a roll or rolls, the pressing is generally carried out by at least one pair of rolls which are arranged over and under a burned or foamed body (hereinafter referred to "foamed body") as shown in Japanese Examined Patent Publication No. 50759/1978. The above-mentioned double-type rolls comprise, as shown in FIG. 13, upper rolls 28a and lower rolls 28b arranged over and under the foamed body, respectively. The foamed body after being foamed and softened is pressed by the upper rolls 28a and lower rolls 28b, whereby both surfaces of the foamed body is provided with uniform sintered surface.
However, in the above-mentioned conventional methods, the porous ceramic panel is pressed and shaped only in a foaming step (in the case of using a belt), or only after the foaming step (in the case of using rolls). In a result, these methods have several problems in the integration, surface smoothness and the like of the produced porous ceramic panels.
That is to say, in the case of using a belt, a porous ceramic panel is pressed in a heating and foaming step. Since heat-foamable inorganic raw materials are foamed within a limited space between a lower conveying belt and an upper pressing belt, the thickness of the foaming body beween rolls disposed in the pressing belt becomes thick due to the foaming pressure. A wave pattern corresponding to a roll pitch is formed on an upper surface of the foaming body. It is not easy to delete the wave pattern, because the foaming body moves in a kiln with a pressing belt and it is pressed by the rolls through the pressing belt. The wave pattern was a serious defect of the products. Further, it is impossible to give a desirable relief pattern on the surface of the products.
On the other hand, in accordance with a method using rolls, a foamed body after foaming step is pressed and integrated by the rolls. After a layer consisting of pelletized foamable raw materials is heated and foamed to expand in such a manner that foamed particles contact one another in a point, an upper surface of the layer is pressed by rolls. In that case, a roll pressure diffuses and does not reach the central portion of the foamed body because of softness thereof. Accordingly, voids formed at cell-interface cannot be broken. Further, the shape of foamed particles at an upper surface cannot be made smooth. Thus, many voids at cell-interface remain unbroken, and they communicate one another to generate open void cells. In a result, there is caused a problem that the heat-insulation and the water-proofness of the panels deteriorate. It is difficult to obtain a good surface smoothness only by the pressing using rolls.
It is an object of the present invention to provide a method of producing porous ceramic panels having superior integration, dimensional accuracy, and surface smoothness.